How to Use a Greenhouse for Winter Gardening (Yes, Even in Freezing Weather) (2024)

Keep your favorite outdoor hobby going year round by using a greenhouse for winter gardening. There are a few specific things you must do to make a greenhouse usable in winter, such as keeping the interior temperature above freezing, but with some specific adjustments made, you can keep the growing season going.

Here's how to use a greenhouse for successful winter gardening.

Can You Use a Greenhouse in the Winter?

Yes, you can use a greenhouse for winter gardening. Depending on what you choose to grow, your greenhouse can operate all winter with very few alterations.

The biggest concern will be raising the inside temperature of the greenhouse to above freezing and allowing some ventilation during the day to keep your plants fully oxygenated (though some plants will be able to keep growing down to 0 degrees). While this might sound like a serious chore, it is not that difficult or expensive, and you can decide how much or how little money you want to invest to make it happen.

Types of Greenhouses That Work Best in Winter

While most greenhouses can be used during the winter, some will be better than others, and some need to be avoided completely, usually due to materials and insulation. It is best to avoid single-walled greenhouses of any type, especially those made of soft PVC sheets. Make sure it has either a pitched roof or a rounded roof to allow for snow to either be easily removed or slide off on its own.

Here are a few of the better types of greenhouses for winter, listed from the least efficient to most efficient:

• Double-walled polyethylene sheet greenhouses: Most reasonably priced consumer greenhouses are constructed from polyethylene (PE) and aluminum or wooden frames. The best available come double-walled, meaning the two sheets of plastic are sandwiched with a thin gap to allow air to act as an insulator. Some models even include ventilation louvers or a hydraulic skylight that raises and lowers when a temperature reaches a certain point.
• Double-walled glass greenhouses: This style is like a PE greenhouses but made with glass. The framing for this type is usually wood or steel to accommodate the weight of the glass. If properly sealed, double-walled glass greenhouses can withstand very low temperatures, as the glass is filled with more air, allowing for greater insulation.
• Half-wood walled greenhouses: This type of greenhouse is a hybrid of wood and PE or glass, usually double-walled. The benefit of this style is that the wooden base can be insulated with commercial insulation.
• Half-brick walled greenhouses: This type of greenhouse is not cheap but can provide you with the most insulation. On top of that high construction cost, electricity is often run to the greenhouse for heating and ventilation.

How to Keep a Greenhouse Warm in Winter

Keeping a greenhouse warm can be expensive or affordable, high-tech or no-tech, and even sustainable. Whatever method you choose, there is no right or wrong as long as it works for you.

No matter what method you choose, you can also heat it further by laying down black landscaping cloth on the floor and benches to absorb sunlight during the day. Aid this by removing snow from the top of the greenhouse to allow maximum light and heat to get it.

Here are three common methods for heating a greenhouse.

Black Water-Filled Barrel

A great trick to affordably raise the temperature of your greenhouse is to place a black barrel filled with water in the greenhouse. The black plastic of the barrel will absorb heat and raise the temperature a few degrees throughout the night. In especially cold areas, place a solar-driven pond pump in the bottom to keep the water circulating to keep it from freezing.

Electric Heater

The easiest but most expensive way to heat a greenhouse is to install an electric heater on a thermostat. Adding the thermostat will keep the heater running at a steady temperature and avoid having the heater when it doesn't need to be.

Compost Bin

Placing a compost bin in your greenhouse is a great environmentally friendly and useful way to heat your greenhouse. Add the right materials, woodchips, manure, green and brown waste, and compost starter, and the bin can reach 100°F. A few weekly stirs will distribute the materials and let their decomposition happen more effectively, creating more heat. The best part is that if you start the composting in the fall, you will have a good amount of homemade compost ready for the spring.

Types of Vegetables to Grow in a Winter Greenhouse

• Kale: Many of the plants that grow best in a winter greenhouse come from the brassica family. Kale is a cool, weather-hardy plant that can be used in salads, soups, and as a stewed green. Kale is one of the few plants that can live in an unheated greenhouse, as long as the temperature does not sink below -21°F.
• Brussel sprouts: Another brassica, brussel sprouts are a great winter hardy plant. If planted in the fall, these little veggies can be harvested in the late to early spring, as they take about three months to mature.
• Spinach: Another brassica, spinach is very cold and hardy and can often be grown in unheated greenhouses. Be on the lookout for varieties that favor cooler weather.
• Potatoes: While potatoes are great cold-weather plants, they are less cold hardy than those listed here. Don't let this stop you from growing them, as their vulnerability to frost can easily be overcome by placing clear plastic sheeting over them in your greenhouse on days below freezing.
• Winter lettuces: There are many varieties of cold weather-loving winter lettuces that will allow you to have homegrown salads throughout the year. Consider rocket or little gem, two cold, hardy varieties that grow quickly, even during winter.
• Cabbage: Back to the brassica theme, cabbage is a terrific crop to grow during the winter that will be harvest-ready just in time for St. Patrick's Day if you plant it in the fall.
• Broccoli: Not an extremely cold hardy, broccoli will do well in a heated greenhouse. Your crop may not be ready for harvesting, but it will be able to be transplanted outdoors by early spring if started in the late fall.
• Bok choi: This Chinese vegetable is great for growing in cooler temperatures and can be used in various dishes. What's best is it can be started in the mid to late fall and be ready for consumption by midwinter, as it usually takes 30 to 40 days to develop foliage.